You can make the following configurations to eBGP:ĪS Override: You can specify that the ASN of a provider is used to override the ASN of a site. You can specify any number of RT values per VPN and specify whether a value is used for VRF import, VRF export, or neither for hub, spoke, and fully-meshed behaviors. You can easily reassign RT numbers to sites within a VPN, if for example, it has been imported or exported by a different application. You can specify your own RT numbers for hub, spoke or fully-meshed sites within a VPN if you do not want to use the default values. In a hub and spoke VPN topology, IP Service Activator generates two RT numbers – one for the hub site(s), generated as indicated above, and one for all spoke sites, generated by incrementing the hub low order number by 1. Management: Works in the same way as hub and spoke, but is used when setting up QoS to ensure connectivity to CE devices Hub and Spoke: One or more hub sites has access to all other sites spoke sites can access the hub only Mesh: All sites have connectivity to all other sites ![]() The connectivity of the VPN can be one of the following: When routes are distributed, any route marked with a particular export route target attribute will be installed in VRF tables marked with the same import route target attribute. Each VRF is tagged with one or more import route target attributes, indicating the VPNs for which it wants to import routes. ![]() Every route that is distributed from a VRF table is tagged with an export route target attribute identifying its VPN. This is achieved by means of route targets. But since a VRF table is not mapped directly on to a VPN, it is necessary to identify the VPN to which each route applies. Routes defined within a PE's VRF tables are propagated to other PE devices within the same VPN. If a site is in multiple VPNs, the VRF table associated with that site contains routes for all the VPNs of which it is a member. Its purpose is to hold the routes that are available to a particular site connected to a PE device. The MPLS labels only have significance between these LSR-peers.Įach PE router maintains a number of separate forwarding tables known as VRF (VPN Routing and Forwarding instance) tables, and each site (that is, each PE interface or sub-interface connected to a CE device) must be mapped to one of those VRF tables.Ī VRF table does not necessarily correspond to a particular VPN. These labels are associated with Forwarding Equivalence Classes (FECs) that define an IP address prefix for an egress point from the network. The packet's path through the network is defined by its initial labeling – subsequent mapping of labels is defined by the initial label allocation.Įach LSR in the MPLS network normally runs a Label Distribution Protocol (LDP) that distributes the labels that are to be used to forward packets across the MPLS network using peer-to-peer negotiation from network edge to network edge. ![]() This label tells switching nodes throughout the network how to process and forward the data. On entry to an MPLS network, one or more fixed-format labels are inserted at the front of each packet. ![]() The routers within an MPLS network that are responsible for label processing are known as Label Switched Routers (LSRs), and the path followed by data is known as a Label Switched Path (LSP). MPLS uses a technique called label switching to forward data throughout the network.
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